They both sail well.
Historic boats seem to show more Schooners, modern boats more Ketches.
In the real world, a ketch is easier to sail as you can easily drop the mizzen, or only use the mizzen depending on conditions. Not so easy with a schooner. Having said that, you may need to drop the mizzen on a ketch to sail close to the wind.
On a model, there are many considerations.
One is how it looks. Historic sailing ketches tend to have a much smaller mizzen than main, which is a less appealing look, in my mind. This is not always the case, but needs to be considered when choosing your sail plan. On more modern ketches they can be similar sized (if the foremast is well forward).
Connected to this, and for sailing, you can add more sail to a schooner by adding triangular topsails, if gaff rigged, and a square topsail on the fore if you so desire.
A schooner will sail closer to the wind more easily. Sometimes on a small lake, it makes a difference if you can tack in tighter spaces, instead of wearing.
Access to the RC gubbins below deck. In plan view (from above) sketch out your sail plan, including the placement of the standing and running rigging. Work out the size of your deck hatches, and think about how easy it will be to put your hand in to change batteries, switch switches, and even remove components if you need to.
Also. There is no reason why you should not use a schooner hull for a ketch and visa versa. In the real world, ships often changed their mast and sail plans over time.